Process for crimping fibers



Jan. 7, 1958 E. w. LE BOEUF 2,818,630

PROCESS FOR CRIMPING FIBERS Filed May 10, 1954 INVENTOR Eayar M4 1.2506112" BY I ATTORNEYS.

United States Patent I 2,818,630 PROCESS FOR CRIMPING FIBERS Edgar W. Le Boeuf, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of This invention relates to a new and useful process for producing crimped fibers. More particularly, it relates to a process for producing a random crimp in continuous synthetic fibers.

For purposes of this application the term fibers should be construed as having the meaning commonly employed in the polymer and synthetic fiber art. In that meaning fibers are fine thread-like, filamentary articles and are differentiated from monofilaments only in being of smaller diameter.

It is well known that continuous fibers may be produced from thermoplastic polymers and copolymers. The fibers are commonly formed by expressing a hot plastic mass through die orifices, followed by supercooling the fibers (when the polymer is crystalline) and then stretching them to orient the fibers along the fiber axis, or by the equally well known wet or dry spinning processes. Many such fibers are circular in cross-section and have a smooth surface. When a yarn is formed from a tow of such fibers by twisting and drawing the tow, the individual fibers are able to slip past each other, when the yarn is under tension, due to their low surface friction. Consequently, the strength of the yarn is appreciably less than the aggregate strengths of its several filaments. It has been the practice in the past to produce periodic bends or crimps in the fibers to minimize their slipping tendency. That crimping was usually achieved by mechanical or chemical means. The mechanical methods, such as passing the fibers between knurled rolls, had the disadvantages that the crimp was uniformly spaced, and that the heat and pressures used frequently distorted and weakened the fibers. The chemical methods usually relied on solvents which would swell or distort the fibers. With those polymeric materials which are highly resistant to solvents, such as the crystalline vinylidene chloride copolymers, those methods are not generally applicable.

It is the principal object of this invention to provide a process for producing a random crimp in continuous fibers.

It is a further object to provide such a process whereby fibers made from normally crystalline vinylidene chloride copolymers may be produced having any desired degree of crimp.

It is a still further object to provide a process whereby the crimping operation may be carried on concurrently with the extrusion or spinning operation.

The above and related objects are accomplished by means of a process consisting of passing a continuous tow of fibers through the nip of a pair of rolls operating at different peripheral speeds. When both rolls are rotating it has been found that the ratio of the peripheral speeds of the rolls should be at least 1.5 :1. The upper limit of the ratio of the peripheral speeds is about 1000:1. Higher ratios may be employed but no additional benefits accrue from such ratios, and in addition the shearing action becomes so great that the fibers are 2,818,630 Patented Jan. 7, 1958 ICC frequently broken. The preferred range of operating speeds is from 200:1 to 600: 1.

It is also possible to employ one rotating roll and one stationary roll, although such an arrangement causes the stationary roll to wear unevenly. This process produces a random crimp in the individual fibers, and in addition opens the tow somewhat, making subsequent handling operations easier. 7

The operation ofthe process of the invention will be more apparent from the annexed drawing and the following description. The drawing represents a diagrammatic cross-section of the apparatus used in carrying out the process of the invention.

A continuous tow is supplied to the crimping apparatus. The tow may be fed directly into the crimping apparatus from the spinning and orienting means or may be fed from a separate supply of fibers.

The crimping apparatus consists of a pair of rolls having zero clearance between them. Each of the rolls is driven, and each at a different peripheral speed from the other. The rolls are smooth surfaced (as opposed to knurled or serrated rolls) but not polished. Although it is not critical to the operation of the process, the rolls are preferably of the same size. One or both of the rolls may be heated, although when fibers made from vinylidene chloride copolymers are to be crimped, no additional benefits accrue by having heated rolls. The fibers are crimped by feeding them between the pressure rolls in the direction of rotation of the rolls.

The continuous tow, after crimping, may be twisted directly into a yarn or may be stapled, opened, and processed into yarn by conventional means.

The differential in the peripheral speed in the rolls produces a rubbing action on the fibers at the point of contact of the rolls. The differential rubbing action appears to stretch one side of each filament more than the other, resulting in a crimped product.

Such a rubbing action has the additional advantage that the tow is opened somewhat so that after twisting a bulky yarn, similar in appearance to yarns from natural fibers, is obtained. The opening also tends to make subsequent tow handling operations easier.

The rubbing action produces an unexpected randomness to the crimp in the fibers. Randomness is necessary to provide the desired resistance to sliding of one fiber past another.

In an illustrative example, a continuous tow of straight uncrimped fibers was prepared by spinning a copolymer consisting of 60 percent vinylidene chloride and 40 percent acrylonitrile from an acetone solution. The tow was 4200 denier and was made up of 2000 straight uncrimped fibers of 2.1 denier per filament. This tow was passed through the nip of two smooth hard-rubber rolls adjusted to zero clearance. The peripheral speed of one of the rolls was 625 ft. per minute and the peripheral speed of the other roll was 1.5 ft. per minute. A randomly crimped tow was obtained. Subsequent passes of the tow between the rolls increased the degree of crimping.

The same effects were observed when each of the several normally crystalline vinylidene chloride copolymers in the form of oriented fibers was passed between the rolls. It was also found possible to produce crimped fibers when continuous tows of acetate rayon, viscose rayon, and nylon were passed between the rolls.

Iclaim:

1. A process for crimping synthetic fibers comprising passing a continuous tow of said fibers between the nip of a pair of driven pinch rolls in the direction of rotation of said rolls; one roll of said pair being driven at a peripheral speed at least 1.5 times that of the other roll of said pair.

2. A process for crimping synthetic fibers comprising passing a continuous tow of said fibers between the nip of a pair of driven pinch rolls in the direction of rotation of said rolls; one roll of said pair being driven at a peripheral speed from 1.5 to 1000 times that of the other roll of said pair.

3. The process claimed in claim 1, wherein one of said rolls is driven at a peripheral speed from 200 to 600 times that of the other roll.

4. The process claimed in claim 1, wherein the fibers subjected to crimping are composed of a normally crystalline vinylidene chloride copolymer.

References Cited in the file of this patent UNITED STATES PATENTS Wrigley et a1. Nov. 26, 1935 Wrigley et al. Feb. 7, 1939 Koga Sept. 3, 1940 Wrigley et a1. Nov. 25, 1941 Bruenner et a1. Feb. 6, 1945 

1. A PROCESS FOR CRIMPING SYNTHETIC FIBERS COMPRISING PASSING A CONTINUOUS TOW OF SAID FIBERS BETWEEN THE NIP OF A PAIR OF DRIVEN PINCH ROLLS IN THE DIRECTIONS OF ROTATION OF SAID ROLLS, ONE ROLL, OF SAID PAIR BEING DRIVEN AT A PERIPHERAL SPEED AT LEAST 1.5 TIMES THAT OF THE OTHER ROLL OF SAID PAIR. 